When patients present with chest pain, palpitations or any other symptoms of coronary trauma or disease, the presence of vascular thrombi in the heart is a potential significant complicating factor for treatment. If a medical practitioner could non-invasively determine whether one or more vascular thrombi were present and, if present, the location of those vascular thrombi, better evaluation of treatment options would be possible. Furthermore, if a medical practitioner could determine that no vascular thrombi were present, thereby eliminating a potential complication in treatment, cardiac conditions could be treated more safely and effectively.
Most present techniques for determining the presence of vascular thrombi are invasive and/or cumbersome, and/or fail to detect such thrombi with good sensitivity and specificity. Thus, an imaging agent useful for non-invasive vascular thrombi imaging is desirable.
Annexins are a class of proteins that are characterized by calcium-mediated binding to anionic phospholipids. Anionic phospholipids are about 20-fold more highly associated with activated platelets than quiescent platelets, and activated platelets are associated with vascular thrombi.
Radioiodinated annexin V has been shown to localize to vascular thrombi in vivo, but has suboptimal imaging characteristics, possibly due to the pronounced beta phase of blood clearance owing to possible transiodination and/or metabolic degradation with reincorporation into serum macromolecules or non-target tissues. Free radioactive iodine or iodine-containing metabolic degradation products exposed non-target tissues, especially the thyroid gland, to radioactivity. Iodine radioisotopes I-123, I-124 and I-131 with imagable photons suffer from various drawbacks. Iodine-131 has particulate emission and its gamma emission is too high in energy for optimal imaging. Iodine-124 emits positrons and high energy gamma photons. Finally, I-iodine-123 radiolabel with superior imaging properties is expensive and difficult to obtain and is not therefore practical for wide spread use. Consequently, improved radiolabeled annexin compounds are desirable.
In addition, conventional imaging and therapy are often plagued by the problem that the generally attainable targeting ratio (ratio of administered dose localizing to target versus administered dose circulating in blood, or ratio of administered dose localizing to target versus administered dose migrating to bone marrow) is low. Improvement in targeting ratio is also sought.
Thus, for the foregoing reasons there is still a need for a thrombus imaging product with increased sensitivity to image small thrombi, such as carotid thrombi or intra-cardiac thrombi and those present in coronary arteries after angioplasty or during myocardial infarctions or in cerebral arteries during stroke. Development of a radiolabeled thrombus imaging agent capable of detecting intracoronary thrombi would represent a breakthrough product of great clinical and commercial significance. The present invention fulfills this need and provides further related advantages.